On the eve of the Republican presidential debate, a nonprofit organization that doesn’t have to disclose its donors released a two-minute online video assailing U.S. Sen. Marco Rubio’s position on immigration reform.

The clip — snippets of Rubio’s interviews and speeches spliced together — was produced by Brave New Films Action Fund, based in Culver City, Calif., and founded by Robert Greenwald, a former Hollywood filmmaker who’s found a second career by releasing left-leaning exposes about the Iraq war, Fox News and Wal-Mart, among other subjects. The group also paid for a 30-second, anti-Rubio TV commercial airing in several states with large Latino populations, Greenwald said in a prepared statement.

“We need someone who will bring the immigration issue to the table in an impactful way and fight for better policies,” Greenwald said. “Rubio parades around as that person, but his record says otherwise.”

Brave New Films demonstrates the growing problem of “dark money,” the term used to describe political spending by tax-exempt 501(c)4 social welfare organizations like Greenwald’s. According to The Daily Dot:

Nonprofits with this designations are free from any obligation to announce where their money comes from. The dark money reaching campaigns rose from $6 million in 2004 to $309 million in 2012.

To qualify for this designation, an organization “must be operated exclusively to promote social welfare,” according to the Internal Revenue Service (IRS). And to do so, “an organization must operate primarily to further the common good and general welfare of the people of the community.” The problem is, many groups that have secured this status qualify for that only if you believe that extremely partisan groups with specific political goals fall under that designation.

On its website, Brave New Films states its purpose is to produce socially relevant and edcuational short videos that timely address pressing social issues.

Robert Greenwald (Photo by JD Lasica/Flickr)

Of course, presidential candidates are supported by 501(c)4 organizations as well. For example, Conservative Solutions Project is a nonprofit that plans on spending more than $1 million airing ads that tout Rubio’s opposition to the Obama administration’s Iran nuclear deal. The nonprofit was established by South Carolina political consultant J. Warren Tompkins, who also started a pro-Rubio super PAC with a similar name that has raised nearly $16 million.

Greenwald said Brave New Films does not support a particular candidate. However, his only intended targets are Republican presidential contenders. According to its website, Brave New Films is raising funds to make similar videos about current front-runner Donald Trump, former Florida Gov. Jeb Bush and Wisconsin Gov. Scott Walker.

According to the nonprofit’s most recent available tax return, Brave New Films received $231,983 donations and grants in 2013. In a 2014 interview with AlterNet, Greenwald said Brave New Films relies largely on modest individual contributions: “We do have some large donors who have specific issues they care about, or care about making sure that Brave New Films survives. And then we have the amazing 20,000-25,000 small donors who give us from $5 to $15 to $100. It’s not cheap. It’s not free. But it’s not the millions that it used to cost to make a film.”

Editor’s note: FCIR has asked the Rubio campaign for a response to Greenwald’s video. We’ll update if the campaign responds.